I checked your example with solar system. Since it's calling directly document.getElementById, it would not be some valid Python code that I could run independently. Isn't that defeating the purpose of coding in Python first?
Purpose of Transcrypt is to be able to use Python in the JavaScript world. The call document.getElementById doesn't have meaning outside a browser. For non-gui debugging purposes module org.transcrypt.stubs.browser is present supporting the bare minimum. Of course someone could write a library supporting all kinds of DOM functions. But I don't think it would be very useful. The idea is to be able to do the whole web "chain" in Python. So CPython + a framework on the server, Transcrypt in the Browser (or, generally, JS client).
It's still valid python code, the libraries are just different.